Multicore Fiber with Distal Motor

ABSTRACT

An optical probe imaging system includes an optical probe with a multicore optical fiber positioned therein. Distal optics are optically coupled to the distal end of the multicore fiber that image light propagating in the multicore fiber so as to generate a light pattern on a sample that is based on a relative position of at least two cores at a distal facet of the multicore fiber. A distal motor is mechanically coupled to the optical probe so that a motion of the distal motor causes the light pattern to traverse a path across the sample. An optical receiver is coupled to the proximal end of the multicore fiber and receives light that has traversed the path across the sample and then generates an electrical signal corresponding to the received light. A processor maps the electrical signal to a representation of information about the sample, wherein the mapping is based on the relative position of at least two cores at the distal facet of the multicore fiber and on the motion of the distal motor.

The section headings used herein are for organizational purposes onlyand should not to be construed as limiting the subject matter describedin the present application in any way.

INTRODUCTION

The present teaching relates to medical and non-medical applications fordelivering and/or collecting light, and/or performing sensing, and/orperforming optical imaging, and/or performing optical therapy of asample at the distal end of an optical waveguide. There are many medicaland non-medical needs for performing optical imaging or sensing of asample (e.g. human organ or other samples in hard to reach places).Relevant optical properties can include, for example, absorption,reflection, refractive index, birefringence, dispersion, scattering,spectral characteristics, fluorescence, thickness, and other properties.In some embodiments, these relevant optical properties can be determinedas a function of wavelength. In addition, the optical properties can bedetermined at a point, in a small volume, and/or can be spatially orspectrally resolved along one dimension, or multiple dimensions.

Single-mode optical fibers are commonly used to transmit light along afiber-based optical instrument. They are well suited for use in severalembodiments of multicore fiber with distal motor according to thepresent teaching as they are both inexpensive and flexible. Butsingle-mode fiber by itself has limited capabilities. For example, toperform imaging using a single-mode fiber usually requires scanning thelight emitted and/or collected from the single-mode fiber. These knowntechniques suffer from a variety of significant limitations such as: (1)the endoscopic or other type of probe being too thick and/or notflexible enough to access important regions within the human body; (2)an inability to fit inside existing ports of clinical and non-clinicalinstruments; (3) the endoscope or optical probe or the system itattaches being too expensive or bulky; (4) the endoscope or opticalprobe being less reliable than desired; and/or (5) the scanningmechanism introducing optical image artifacts, such as non-uniformrotation distortion. A significant advance over these limitations inprior art fiber-based instruments is needed to open up new clinical andnon-clinical applications and to improve performance in existingsystems.

BRIEF DESCRIPTION OF THE DRAWINGS

The present teaching, in accordance with preferred and exemplaryembodiments, together with further advantages thereof, is moreparticularly described in the following detailed description, taken inconjunction with the accompanying drawings. The person skilled in theart will understand that the drawings, described below, are forillustration purposes only. The drawings are not necessarily to scale,emphasis instead generally being placed upon illustrating principles ofthe teaching. The drawings are not intended to limit the scope of theApplicant's teaching in any way. Also note for simplicity some of thedrawings show beam propagation (e.g. beam divergence) that is not toscale or proportion or exact location within the samples.

FIG. 1 illustrates a block diagram of a known optical probe system.

FIG. 2A illustrates an embodiment of an optical probe system with amulticore fiber of the present teaching.

FIG. 2B illustrates an embodiment of a portion of an optical probesystem with a non-planar folding element of the present teaching.

FIG. 3 illustrates an embodiment of an optical probe system with amulticore fiber that implements optical coherence tomography imaging ofthe present teaching.

FIG. 4 illustrates an embodiment of an optical probe system with amulticore fiber that converges optical beams at a central axis of arotating motor of the present teaching.

FIG. 5 illustrates an embodiment of an optical probe system with amulticore fiber and a hollow motor of the present teaching.

FIG. 6 illustrates an embodiment of an optical probe system with amulticore fiber and configured for forward imaging of the presentteaching.

FIG. 7 illustrates an embodiment of an optical probe system with adistal scanner of the present teaching.

FIG. 8 illustrates an embodiment of imaging a human eye using an opticalprobe system of the present teaching.

FIG. 9A illustrates another embodiment of imaging a human eye using anoptical probe system of the present teaching.

FIG. 9B illustrates an embodiment of a scan pattern of a single core ofthe present teaching.

FIG. 9C illustrates an embodiment of a scan pattern of multiple cores ofthe present teaching.

FIG. 9D illustrates an embodiment of a scan pattern of multiple coreswith a rotation of the present teaching.

FIG. 10 illustrates an embodiment of an optical probe system includingand X-Y scanner and optical switch of the present teaching.

DESCRIPTION OF VARIOUS EMBODIMENTS

The present teaching will now be described in more detail with referenceto exemplary embodiments thereof as shown in the accompanying drawings.While the present teaching is described in conjunction with variousembodiments and examples, it is not intended that the present teachingbe limited to such embodiments. On the contrary, the present teachingencompasses various alternatives, modifications and equivalents, as willbe appreciated by those of skill in the art. Those of ordinary skill inthe art having access to the teaching herein will recognize additionalimplementations, modifications, and embodiments, as well as other fieldsof use, which are within the scope of the present disclosure asdescribed herein.

Reference in the specification to “one embodiment” or “an embodiment”means that a particular feature, structure, or characteristic describedin connection with the embodiment is included in at least one embodimentof the teaching. The appearances of the phrase “in one embodiment” invarious places in the specification are not necessarily all referring tothe same embodiment.

It should be understood that the individual steps of the methods of thepresent teaching can be performed in any order and/or simultaneously aslong as the teaching remains operable. Furthermore, it should beunderstood that the apparatus and methods of the present teaching caninclude any number or all of the described embodiments as long as theteaching remains operable.

The present teaching relates to the many medical and non-medicalapplications for delivering and/or collecting light and/or performingoptical imaging of a sample in hard to reach places. In this disclosure,the word “light” is intended to be a general term for anyelectromagnetic radiation, for example, in the wavelength range fromultraviolet to infrared, including the entire visible spectrum. Also, itshould be understood that the terms “waveguide” and “fiber” are usedinterchangeably in this disclosure as an optical fiber is a type ofwaveguide. It should also be understood that the term “endoscope” asused herein is intended to have a broad meaning to include medicaldevices such as catheters, guidewires, laparoscopes, trocars,borescopes, needles, and various minimally invasive and robotic surgicaldevices. In addition, the present teaching is not limited to use inendoscopes but, in fact, has a wide variety uses in fiber-basedinstruments that are housed in numerous types of packages and apply to avariety of illumination and/or measurement and sensing applications.Examples include ophthalmic imaging apparatus, and surgical and othertypes of microscopes, tethered capsules, and swallowable capsules, andother devices. A few of such examples are shown in the figures anddescribed herein.

It should be understood that the word “fiber” and the word “core” areused throughout the specification in a somewhat interchangeable manner.In particular, it should be understood by those of skill in the art thatwhen multiple cores are described as embedded in a common cladding,there is an equivalent embodiment with multiple optical fibers, eachwith a core and a cladding embedded in a second outer common cladding.Such cores could be single-mode, few-mode, or multi-mode optical cores.

There are numerous medical and non-medical applications of opticalranging, sensor, or imaging devices and systems including in cardiology,gastroenterology, pulmonology, laparoscopy, ophthalmology, industrialinspection, NDE/NDT, 3D printing, and LiDAR applications. There are manytypes of rigid and flexible delivery optical mechanisms includingendoscopes, catheters, imaging guidewires, laparoscopes, borescopes,swallowable pill capsules, swallowable tethered capsules, imagingneedles, X-Y scanning mirror scanning systems used in ophthalmology,microscope, and other applications and other approaches used to relayoptical or other information from a distal location to a proximallocation. The description that follows, will most often be described byreferring to an optical probe (and occasionally other similar words) butit should be understood that it is equally applicable to these othertypes of medical and nonmedical instruments. The words “sample”,“target,” and “tissue” will often be used interchangeably in the textbelow. Also, often the word “imaging” will be use to describe thisinvention but it should be understood that this invention is equallyapplicable to sensors, ranging, therapeutics, interventional, and otheroptical and electrooptical systems and applications.

Often the word distal motor will be used. This term can reflect a widevariety of types of motors including rotational motors, X-Y scanninggalvanometers, translating fibers, translating lenses, MEMs devices,electromagnetic devices, PZT motors, and may other types of motors.

There are many approaches to transferring imaging, ranging, or sensoroptical information along an optical probe including utilizingsinglemode or multimode fibers, fiber optical bundles, mechanical orelectro-optical scanning elements, sets of relay lens, and graded indexlenses. For example, the concept of using a single core fiber and adistal spinning motor and a pullback device has been described in theliterature and is in common use today in, for example, intravascular andgastrointestinal optical coherence tomography. In general, the term“pullback” may be used to refer to either of both of backward andforward motion of a probe with respect to the sample, unless a directionis specifically indicated.

It should be understood that many of the figures described in thefollowing paragraphs are drawn to illustrate concepts and embodiments ofthe present teaching, but are not necessarily drawn to scale and oftenthey are simplified drawings omitting known structural and functionalelements and/or simplifying optical beam propagation in a way that isknown to those skilled in the art. Furthermore, some text descriptionsand figures will describe light emanating from a source through amulticore fiber that is directed to and being altered by lenses andother optical elements and impinging on a sample or target. It should benoted by reciprocity that often the reverse path where light iscollected on a sample and directed to a receiver is equally suitableeven if it is not explicitly mentioned.

FIG. 1 illustrates a block diagram of a known optical probe system 101.The optical probe system 101 includes a system controller 102 connectedto a patient interface unit 103. The optical probe system 101 canoptionally include a pullback mechanism. The optical probe system 101includes a single core optical fiber 104, distal optics 107 and arotating distal motor 110. The single core optical fiber 104 is shownboth as part of the probe system 101 and as an expanded view. Theoptical probe system 101 contains several subsystems. There is anoverall system controller 102 that can contain computation (computer),display, storage, power supplies, networking interfaces, an opticalsource, optical receiver, and various other optical, electrical, andmechanical items. There is a patient interface unit (PIU) 103 that hasoptical, electrical, and mechanical connections to controller 102. Thepatient interface unit 103 is also connected to an optical probe 106.There can be various permanent, semi-permanent, and/orattachable/removable optical and electrical and mechanical connectionsbetween the controller 102, the PIU 103, and optical probe 106.

There are also structural, optical, and/or electrical connections (notshown) within the optical probe 106 to hold, support and operate thedistal folding element 109 and its associated motor 110 and other partsof optical probe 106. They are not shown in any detail for simplicity asthey are known in prior art. The optical probe 106 is shown in asimplified view and contains many structural and mechanical and otherelements to support the reliable and smooth operation to navigatetorturous channels within the human body or in non-medical applications.

The optical probe 106 also contains a single core optical fiber 104. Theoptical fiber 104 may be enclosed in a structure element 105 to provideadditional strength and reliability and/or allow it to be manipulated.For example, the structure element 105 may be a jacket or a buffer ortorque coil or other element. At the distal tip of the single coreoptical fiber 104 is a distal optical element 107 that, in part,controls the properties of the light emitted to and/or collected fromthe distal target or sample (sample not shown). The distal opticalelement 107 may include one or more optical elements. Also, a foldingelement 109 is positioned at the distal end of the optical probe 106.The folding element 109 is connected to a distal rotational motor 110.The folding element 109 may include a mirror (e.g. a fold mirror) orother optical elements.

System controller 102 is electrically and mechanically connected to themotor 110, though this connection is not shown for simplicity. Thesystem controller 102 controls and supports the rotation of the foldingelement 109. The system controller 102 is connected to the PIU 103. Insome embodiments, the PIU 103 contains a pullback motor (not shown) toallow the optical probe 106 to be pulled back, or advanced, along thelongitudinal axis (z-axis). In some embodiments, operation the PIU 103pulls the single core optical fiber 104, distal optics 107, androtational motor assembly 110 and associated folding element 109 as aunit. In some embodiments, a motor in the PIU 103 can pull the opticalprobe 106 along an outer concentric sheath 120. In some embodiments, theouter concentric sheath 120 is an outer housing. The outer concentricsheath 120 is only shown conceptually shown by the dotted line in FIG. 1. The outer concentric sheath 120 may be formed by materials surroundingthe probe, and may not always be physically part of the probe orattached to the probe. Examples of an outer concentric sheath 120include within gastrointestinal tissue lumens, coronary arteries, orwithin accessory port of another optical probe such as an endoscope. Insome embodiments, the PIU 103 does not contain a pullback motor and theprobe is manually manipulated longitudinally. An example of this wouldbe a system such as a tethered capsule esophageal application.

In operation, system 101 can perform a helical scan or other type ofscan within a lumen, solid organ, or other areas within the human bodyor other medical or non-medical specimens. The helical scan is shownconceptually in inset illustration 111. The relative spacing and pitchof the helix is set by the controller and is in part determined by theratio of the pullback speed to the rotation speed.

Inset illustration 112 illustrates the unwrapped view. This insetillustration 112 is a diagram of a coordinate-transformed representationof the helical scan illustrated in inset illustration 111. The unwrappedview shows the cylinder shown in inset illustration 112 as cut openalong the z axis and thus the helical scan is unwrapped and projectedonto the surface shown in the inset illustration 112. The spot 113 showswhere the light 108 emitted from the optical probe 106 interacts with asample (not shown). The light 108 originates from an optical source (notshown) in the controller 102, and propagates to the distal end of theoptical probe 106 along single core fiber 104 and then to distal optics107. After exiting the distal optics 107, the light 108 reflects, or isotherwise directed out of the probe 106 by the folding element 109. Thelight 108 passes through the transparent outer sheath 120 and impingeson the sample at spot 113. The light may also be collected by the sampleat this spot 113. In some embodiments, an optional optical window (notshown) is provided in the optical probe 106 and the light 108 passesthrough that optical window. A line 114 shows the conceptual path a spot113 would take along a sample, in the unwrapped view, during a helicalscan along the sample. The sample could be, for example, a humancoronary artery, vein, bronchial branch, colon, ureter, esophagus, solidorgan, etc.

One of the limitations of the known probe system 101 is that the imagingspeed can be relatively slow. Increasing the imaging speed can beimportant in many medical and non-medical applications, such as: (1) toreduce motion induced artifacts from things like breathing, the beatingof the heart, or other motion or vibrational disturbances that cancorrupt sensor or imaging information; (2) to perform speckledecorrelation angiography; or (3) to minimize the time blood must beflushed out of the coronary artery to allow imaging. Further there hasbeen a tremendous amount of work on intravascular optical coherencetomography systems to perform fast imaging within the coronary artery tolocate vulnerable plaques that could rupture and cause a heart attack orother complications, which is useful for performing pre or postassessment of stent placement, etc.

Flushing the blood away from an imaging beam is important forintravascular optical coherence tomography (OCT) but problems can ariseduring the time the heart is not receiving blood due to this flushing.Similarly, in the esophagus imaging speed is very important because theesophagus is very large and to cover all that area can require tens ofgigabytes of data and take many minutes to scan with high resolution.Motion induced artifacts are very difficult to eliminate during thistime with the approaches and implementations of prior art systems. Thisadds to operational costs and procedure and analysis time and makes itextremely difficult to do things like extracting maps of microvesselsthrough speckle decorrelation angiography or Doppler imaging. Forexample, to do angiography requires high density sampling of tissuewhich is in contrast to scanning a very large tissue area such as theesophagus. What is clearly needed in cardiovascular, endoscopic, as wellas other medical and nonmedical applications is a way to increase theimage speed even further and to allow for higher quality images andadditional sample information to be obtained such as OCT, angiographic,NIR, fluorescent, or Raman imaging.

One feature of the present teaching is that it increases the speed ofimaging or sample information generation as compared to prior artoptical probe systems. FIG. 2A illustrates an embodiment of an opticalprobe system 201 with a multicore fiber 204 of the present teaching. Thesimplified block diagram of FIG. 2A illustrates a system controller 202connected to a PIU 203 with a pullback capability. The PIU 203 isconnected to an optical probe 206 that contains a multi core opticalfiber 204, surrounded by structure element 205, with distal optics 207at the distal end of the multicore fiber 204. There is a folding element209 attached to a distal motor 210, that may a rotating motor.

Note that folding element 209 and related items in subsequent figures,e.g. FIGS. 2B-6 , is referred to as a “folding element”, however it isunderstood that a wide variety of beam deflector elements are possible.This includes, for example, reflective, transmissive, refractive ordiffractive elements, elements with planar surfaces or surfaces withoptical power (e.g., for focusing or astigmatism correction) that areanticipated by the present teaching. Also, it should be understood thatalthough a rotational motor 210 is frequently described herein there areother types of motors that can be utilized in embodiments of the presentteaching. This includes, for example, motors that rotate back and forth(as opposed to operating continuously in one direction), forward imagingmotors, displacement motors that are moving optical elements (e.g. atranslating lens system), electrostatic or voice coil motors, and magnetmotors that vibrate the tip of the multicore optical fiber, etc. Animportant feature of the present teaching is the recognition that apredetermined motion of a motor produces a predetermined traversed pathof an optical sample spot that can be used to transform collectedoptical signals from an optical probe system to produce a desiredmeasurement, sensor information and/or image of a sample.

As contrasted to the known optical probe system 101 of FIG. 1 , theoptical probe system 201 of the present teaching uses a multicore fiber204 instead of a single core fiber 104. The multicore fiber 204 may be a7-core fiber, as shown, but other numbers and configurations of coresare anticipated by the present teaching. In some embodiments, the coresare single mode cores, in other embodiments, the cores are multimodecores and, in yet other embodiments, the cores are a combination ofsingle mode and multimode cores. In one embodiment, there are singlemode fibers in a common cladding that have no or weak coupling of lightas it propagates in the fiber from one core to another. In someapplications, it is preferable to use single mode cores, for example inoptical coherence tomography. In other applications, multimode fiber ora combination of singlemode and multimode fiber cores can be used tomake up the multicore fiber.

There are many possible fiber configurations. In some embodiments, thecores are separate and share a common cladding (as shown in FIG. 2A). Insome embodiments, the multicore fiber 204 can contain cores withincores. A notable difference between the known optical probe system 101of FIG. 1 and the optical probe system 201 of the present teaching isthat instead of one light beam between distal optical element and thesample or target, the multicore fiber 204 generates light 208 with sevenseparate light beams (only three are shown). In various embodiments, thenumber of beams may or may not be equal to the number of cores, but ingeneral, it should be understood that more than one beam can be emittedfrom and/or collected by the multicore fiber in the optical probesystems of the present teaching. The optical probe system 201 is used toperform optical measurement of a sample. The sample can be any of a widevariety of elements and can also be referred to as a target, tissue, orother element. Various kinds of samples, targets, tissues and/or othermeasured elements are described herein as examples, but should not beconsidered as limiting the inventive subject matter in any way.

The inset illustration 212 shows an unwrapped view of how the opticalprobe system 201 of the present teaching interacts with a sample.Optical probe systems 201 of the present teaching have optical samplespots. These optical sample spots are spots with particular size, shape,and/or position and each optical sample spot is associated with aparticular core in the multicore fiber 204. Specifically, the size,shape, and/or position of a particular spot has a direct relationship toa size, shape, and/or position of a core in the multicore fiber.Depending on the type of measurement, or the application being realizedby the optical probe system 201, these optical sample spots mayrepresent illumination from the multicore fiber and impinging on thesample, illumination from the sample collected by the multicore fiber,or some combination of light provided to or collected from the sample.

Each optical sample spot also has an associated path that is traversedacross the sample. The path traversed across the sample by a spot has adirect relationship to a motion that is provided by the motor 210 and/orthe pullback mechanism provided by the PIU 203. The path is alsodependent on the position, size, and/or shape of the core and/orintervening optics.

Continuing with the comparison between the prior art optical probesystem 101 of FIG. 1 , the optical probe system 201 of the presentteaching, referring to the unwrapped representation depicted in theinset illustration 212, instead of one optical spot 113, there is apattern 215 of seven optical spots including center spot 213 and anouter spot 220. A line 214 shows a conceptual path central spot 113would take along a sample, in the unwrapped view, during a helical scanalong the sample.

Different embodiments will have different patterns 215 of optical samplespots that relate to the pattern of the cores of the multicore fiber.The optical sample spots will have different shapes, different sizes,and different positions that are related to the shapes, sizes andpositions of the cores of the multicore fiber. Thus, there is a directcorrespondence between an optical sample spot at the sample position anda core of a multicore fiber. The relationship between a shape, size,and/or position of an optical sample spot and a shape, size, and/orposition of a core is also dependent upon other factors, including thedistal optics 207 and folding element 209. The relationship may or maynot be the same for each core and optical sample spot, depending on theintervening optics. However, the relationship is known and predeterminedfor particular embodiments of the optical probe system 201 and thus, canbe used to transform data collected from a sample into usefulmeasurement information. Furthermore, as the pullback and/or rotationalmotions of the optical probe system 201 progress, each spot willtraverse a path that corresponds to a corresponding position, sizeand/or shape of a core in the multicore fiber. Thus, there exists apredetermined relationship between a motion of the optical probe and apath traversed by the optical sample spots associated with the cores andthus, the relationship can be used to transform data collected from asample into useful measurement information.

Specifically, as the rotational motor 210 rotates, the folding element209 and the pullback (or push forward) mechanism in PIU 203 can beactivated (or pullback is manually performed), a scan pattern within thelumen (or other sample/target structure) is initiated. This scan pattern215 can cover more area in the same amount of time, thus improving thespeed of obtaining a measurement by the optical probe system. This scanpattern allows additional and/or multiple measurements, sensor, orimaging functions to be performed by the optical probe system 201 at asame time or at different times. As described herein, the pullbackmechanism can be a motorized mechanism and/or the pullback mechanism canbe a manual mechanism.

Detailed mathematical descriptions of the beam transformations relatingthe propagation of light from the distal end of the optical probe 206 tothe sample (e.g. 212) of FIG. 2A are shown below the Appendix. Thesetransformation calculations serve to aid one skilled in the art tooptimize performance for a wide variety of applications. In general,optical probe systems of the present teaching have a predeterminedtransformation that is based on a configuration of the cores in themultimode fiber and the particular motion provided by the optical probe206. Using the predetermined transformation, the controller 202 is ableto provide a desired optical measurement, sensor, or imaging functionbased on light that is present within one or more optical sample spotsat a sample.

There are numerous design tradeoffs that arise from the combination ofmotion and multicore fiber illumination and collection in the opticalprobe system 201 of FIG. 2A. For example, the scan pattern in thepresence of rotation of motor 210 and pullback in the PIU 203 isdifferent from the simple helical pattern in the prior art optical probesystem 101 of FIG. 1 . As compared to the patterns illustrated in insetillustration 111 and inset illustration 112 of FIG. 1 , the sixcircumferential light spots in the pattern 215 illustrated in insetillustration 212 will rotate around the center spot 213 as the motor 210is rotated. The resulting mathematical relationships are described indetail in the appendix. The effect is conceptually illustrated by thedifferent fill patterns in the spots of pattern 215 in insetillustration 212 and the light lines that illustrate the trajectories ofthe spots in the pattern 215 in the inset illustration 212. For example,it can be seen that the tightly dotted fill pattern on the target ininset illustration 212 at the 0° rotational motor rotation point, outerspot 220, has rotated 180 degrees relative to the center full darkfilled spot once the motor has rotated 180 degrees, translated outerspot 220′.

As a comparison of inset illustration 112 and inset illustration 212shows, more area can be covered by the optical probe system 201 of thepresent teaching. Also, the scan pattern that results from thetranslation of pattern 215 is more complex which allows for a richerdata set and a richer measurement and/or sensor and/or image function.

For example, some regions are visited more than once but, at differenttime periods because, for example, spots associated with differentoptical cores visit the same sample spot at different times. The factthat the same sample spot (or, in some cases, approximately the samespot) is visited more than once can allow for benefits such as averagingto improve image quality, detection of motion via speckle decorrelation,and many other benefits to extract additional information out of thesample, tissue, or target. Thus, one feature of the present teaching isto configure the shapes, sizes and/or positions of at least two cores inthe multicore fiber such that a particular spot on a sample is visitedby an optical spot that corresponds to the first core and an opticalspot that corresponds to the second core at a different time consideringat least one of a relative motion of the optical probe 206 and/or arelative motion of a folding element 209 in the optical probe 206.

There are many design variables that can be used in the optical probesystem of the present teaching to improve performance as compared toknown optical probe systems that utilize single cores. These includedesign variables that are suited to specific applications and/or sampletypes. These also include design variables that are suited to improve aperformance of a particular application. Some examples of designvariables include the geometry of the multicore fiber, the number ofcores, the size of the cores, and/or their relative spacings. Thesevariables can be used, for example, to change the shapes, sizes, andpositions of the resulting optical sample spots as well as how theoptical sample spots may change as a result of probe motion. Some or allof the cores can be single mode cores. Some or all of the cores can bemultimode. In addition, some or all of the cores can be few-mode cores.The various different types of cores will affect the amplitude andphase(s) of the provided and/or collected light that propagates in thecores.

Another important design variable is the imaging properties of thedistal optics and how the light emitted and/or collected from themulticore fiber is imaged onto and/or collected from the sample. Thesedesigned imaging properties will affect, for example, spot sizes, focalplane positions, spot shapes of the optical sample spots. In someembodiments, a different imaging function is provided for differentcores. In some embodiments, the same imaging function is provided fordifferent cores. In some embodiments, a single imaging function isperformed on multiple cores.

Another important design variable is the angle of the folding element209 normal relative to the longitudinal axis of the optical probe. Theembodiment of FIG. 2A shows the folding element 209 arranged to deflectthe beam approximately 90 degrees but the mirror normal angle can bemore or less in various configurations.

Another important design variable is the optical properties of thefolding element 209, which can be embodied in as a reflective or arefractive device. The folding element 209 can also have a flat surfaceor have optical power that provides focusing properties.

Another important design variable is the relative speed of therotational motor compared to the pullback motor. The speed of rotationand/or speed of pullback determine the traversed paths for the opticalsample spots. Thus, these speeds impact the transformations that areutilized by the control system 202 to produce a measurement result froma collection of light in an optical sample spot by the cores of themultimode fiber 204 of the present teaching.

For example, in one embodiment, it is desirable to have minimal gaps inareas where the sample is not imaged. Referring to the insetillustration 212 in the example of FIG. 2A, the pullback rate can bedecreased and/or the optical spot sizes on the sample can be madebigger, or the radius of the six spots surrounding the central spot 213can be made bigger. The result is less imaging gap along the tissue, ormore cores can be added to the multicore fiber 204. Thus, a rate ofmotion can be provided that provides a desired image gap along a sample.Also, a core size of at least two cores can be provided that provides adesired image gap along a sample. Also, a number of cores can beprovided that provides a desired image gap along a sample.

The distal optics 207 is used to shape and direct the light from thedistal end of the multicore fiber 204. A variety of lenses and lenspositions with respect to the core(s) in the multicore fiber can be usedto direct the light from the distal tip of the multicore fiber to andfrom the sample. For example, the distal optics can include singleelement lenses, multielement lenses, lens groups, lens-let arrays,prisms and lenses, ball lenses, singlecore and multicore fiber lenses,and/or other optical elements. In one embodiment according to thepresent teaching that is particularly well-suited to single-mode cores,the distal optics includes 3D printed optics on the distal tip. The 3Dprinted optics can include a beam expansion region positioned betweenthe multicore fiber distal facet and a distal optical-powered lenssurface. This allows light from each core to expand via diffraction inthe beam expansion region. The beams expand a small amount. In someembodiments, the beams do not overlap. In some embodiments, the beamsoverlap a small amount. The use of an expansion region allows, forexample, larger beam diameter and thus results in longer focal lengthsof optical beams provided by the cores. The expansion region alsoaccommodates an angled facet at the distal end of the multicore fiber204 so that this exit facet has minimal undesirable back reflections.

In some embodiments, 3D printed individual small lenses (or lenslets)are placed in the path of each core to focus the light onto, and/orcollect light from, the distal target (e.g. coronary artery oresophagus). There are many possible combinations of lenses andassociated fiber cores. In other embodiments, lenslets are not used anda single lens or lens group is used (an example embodiment of this isdiscussed below) to focus light from multiple cores.

FIG. 2B illustrates an embodiment of a portion of an optical probesystem 251 with a non-planar folding element of the present teaching.The embodiment of FIG. 2B illustrates a non-planar folding element 209′that collects light from the distal end of a multicore fiber with angleddistal facet 204′. In this embodiment, the distal optical element can beeliminated (or simplified) and the folding element 209′ comprises amirror that both redirects the light and provides the focusing of thelight by having an appropriate non-flat surface (e.g. a concavedsurface). For simplicity, only one emitted beam from the multicore fiberis shown as 208′, but it should be understood that in most embodimentsthere is a light beam emitted and/or collected from each core of themulticore fiber. This implementation is also a very substantialimprovement over the prior art, even if only one fiber core is used asillustrated in FIG. 2B. Such a configuration eliminates the more complexdistal optics and, consequently is more compact and easier and lessexpensive to manufacture. In some embodiments, the output facet of themulticore fiber is cleaved a right angle to the axis of the fiber. Inthe embodiment illustrated in FIG. 2B, the distal end of a multicorefiber with angled distal facet 204′ is cleaved at a sufficient angle(e.g. seven degrees for a 1310-nm singlemode fiber core) such that thisimplementation can have very little back reflection from the distal tiparea and mainly collect light from the target. This feature is importantin high sensitivity optical imaging and sensing applications like OCT,NIR, and other modalities. There are a variety of methods that can beused to accommodate the slight deviation of emission angle relative tothe multicore fiber axis due to the angled facet (dictated by Snell'slaw). These methods include offsetting the center of the fiber relativeto the axis of the probe or motor, tilting the distal tip of themulticore fiber at an angle, and adding additional optical elements. Itcan also be possible to provide some astigmatism correction from theaberration effects of the outer transparent sheath of the optical probe(not shown) by adding additional distal optical elements in the lightpath or preferably in the design of non-planar surface of fold mirror209′. The correctable aberration can also be caused by an exit windowaround the exit points of beams 208′.

Having a reliable indicator of angular position of the distal motor 210can be an important factor, especially in high speed small motors. Thisangular position is needed in order to reliably know where the beam ison the target. For some motors, the electrical signal that drives themotor can be a reliable indicator of the position. For other motors aonce-per-revolution or multiple-pulse-per-revolution angular encoderconnected to the motor can aid in more precise angular locationidentification. Another method suitable for many endoscopic and otherapplications is to place fiducials on an outer concentric sheath orhousing (not shown). The fiducials effect the optical beam transmittedand/or received by absorbing, scattering, or altering the beampropagation through the fiducial. Then, using signal processing, theadjacent angular scans can be aligned to the fiducials by lining them upafter imaging reconstruction. Another approach is to use informationfrom the target itself such as the inherent speckle. Non-uniformrotational distortion (NURD) is known to be correctable using these andother approaches. Similar approaches can be used in the longitudinaldirection (e.g. pullback), however, it is easier to have a preciseencoder on the longitudinal motor as there is typically more room in thearea of the PIU 203. For X-Y scanning galvanometers, it is common tohave encoders as a reliable indicator of mirror position and oftenfeedback loops are incorporated in the drives to ensure minimal errorbetween commanded position and actual mirror position.

While the descriptions provided herein generally refer to illuminationthat emanates from the probe and is projected toward the sample, it isunderstood that the system according to the present teaching may operatewith all or some light emanating from the sample and the optical probeacting as a collection system. Combinations of these differentdirections are also anticipated. The principles of operation of thepresent teaching are generally reversible, and the probe can operate ineither and/or both directions, as understood by those skilled in theart.

One feature of the present teaching is that numerous types of opticalimaging, sensing, or ranging applications that can be implemented by themethods and apparatus of the present teaching. Referring to FIG. 2A, forexample, the system controller 202 can produce time domain, spectraldomain, or swept source optical coherence tomography or other types ofinterferometric imaging, near infrared imaging, spectroscopic imaging,diffuse wave imaging, Raman imaging and sensing, and fluorescenceimaging or sensing, and various combinations thereof. In someembodiments, different cores, or sets of cores implement different typesof application. In other embodiments, all or most cores are usedtogether to support a particular application.

FIG. 3 illustrates an embodiment of an optical probe system 301 with amulticore fiber 304 that implements optical coherence imaging of thepresent teaching. The optical probe system 301 includes a systemcontroller 302 connected to a patient interface unit 303 with a pullbackcapability, an optical probe 306 containing a multicore optical fiber304 surrounded by structure element 305 with distal optics 307, and arotating distal motor 310. The optical probe system 301 uses sweptsource optical coherence tomography with parallel receivers 334. A sweptsource laser 330 is coupled to the PIU 303 and the system controller 302is configured such that the optical probe system 301 implements anoptical coherence (SS-OCT) imaging system. An inset illustration showsthe unwrapped view of the trajectory of the pattern of spots 315associated with the cores of the multicore fiber 304 during a helicalscan caused by a combination of the pull back of the probe 360 and therotation of the folding element 309 by the motor 310. A line 314 shows aconceptual path central spot 313 would take along a sample, in theunwrapped view, during a helical scan along the sample.

The control system 302 is positioned at the proximal end of the opticalprobe and contains all the control and computation, display, and otherfunctions that are customary in SS-OCT systems. In particular, thecontrol system 302 contains a swept source laser 330 that is opticallycoupled to a beam splitter 331. The beam splitter 331 directs light toboth a reference arm unit 332 and to each of a plurality of circulators333. Each circulator 333 is optically coupled to one single mode core ofthe multicore fiber 304. In some embodiments, one or more of the coresthat are optically coupled to a circulator 333 is a few-mode fiber. Eachcirculator is also coupled to a receiver 334. Optionally, beam splittersmay be used instead of circulators 333. The reference arm unit 332 maycontain an optional adjustable delay to approximately match the opticalpath length in the sample and reference paths as is known in the art ofSS-OCT. Alternatively, it is possible to use one of the cores in themulticore fiber 304 as some or all of a reference path. If one of thecores in the multicore fiber 304 is used as some or all of the referencepath, a reflection from at or near the distal end reference core of themulticore fiber 304 can serve as part of the reference path. One featureof this configuration is that implicitly the length and dispersion arenearly matched between the reference and sample paths within themulticore fiber 304, which makes manufacturing easier since tighttolerances on length of the probe 306 are relaxed.

In the SS-OCT optical probe system 301 of FIG. 3 , there are shownmultiple receivers 334 that detect light in parallel. Although not shownin FIG. 3 , it is possible to use a single receiver to receive thereference signals and the light that emerges from the circulators 333.In some embodiments, an optical switch is used to pass light from themultiple cores to the receiver. In some embodiments, one or more timedelays are provided between the light that emerges from the circulatorsand the receiver and, the different optical channels are detected usingdistinct delays in each sample path (or reference path) that emergesfrom the multicore fiber 304. Each different optical channel can beprocessed separately using the fact that each will have a distinctelectrical frequency band. There is a digital signal processor 335connected to the receivers (or receiver) to extract imaging and otherinformation.

Cost and/or size are important in virtually all applications. Tominimize cost and/or size, it can be highly beneficial to use one ormore photonic integrated circuits (PIC) to realize many of the opticalfunctions shown in the diagram of the control system 302. For example,in embodiments in which the receivers 334 are coherent receivers, itpossible to put multiple coherent receivers, with associated opticalwaveguides and integrated photodetectors on a single PIC. Many othercombinations of optical functions can be combined on a PIC to realizeany of size, cost, complexity and/or performance advantages.

In some embodiments, it is possible to have an additional motortranslating (not shown) the distal end of the multicore fiber 304 shownin optical probe 306. It is known in the art that the lateraltranslation of a fiber relative to the axis of a lens can cause lightemitted scan relative to the axis of the lens. It is also possible totranslate a lens and have a fixed fiber. One feature of using anadditional motor in a multicore fiber configuration is that multiplereceivers can be used to dramatically increase the speed of acquisition.This is because there is an increase in area coverage and the potentialof multiple receiver configurations. Such a configuration also allowsfor the collection of additional information such as light emitted fromone fiber being collected in another fiber. It should be understood thatthe use of an additional motor is not limited to the embodiment of FIG.3 , and applies generally to various embodiments described herein.

It should also be understood that although FIG. 3 is described withrespect to a swept source OCT system, it is equally applicable toimplementation of a spectral domain OCT system or other types of opticalsystems. Also, an alternative embodiment described later in connectionwith the description of FIG. 10 uses a single receiver and a fastoptical switch. This embodiment is described with respect to a forwardX-Y scanner embodiment but such an embodiment is equally applicable toan optical probe like implementation with a rotating distal motor suchas the configuration shown in FIG. 3 .

FIG. 4 illustrates an embodiment of an optical probe system 401 with amulticore fiber 404 that converges optical beams 408 at or near thecentral axis of a rotating motor 410 of the present teaching. Theoptical probe system 401 includes a system controller 402 connected to apatient interface unit 403 with a pullback capability. An optical probe406 contains a multicore optical fiber 404, surrounded by structureelement 405, with distal optics 407 and a rotating distal motor 410. Thedistal optics 407 emits and/or collects light that converges near thecenter axis of the distal motor. The light 408 emitted (or impinging)onto the cores of multicore optical fiber that are positioned off thecentral axis of the multicore fiber follows a path with a slight anglerelative to the longitudinal axis of the optical probe 406 such that thevarious light beams converge near, or even at, the center of therotating folding element 409. The folding element 409 may be a flatmirror angled at 45 degrees from the longitudinal axis of the probe insome embodiments. The fact that the beams converge near, or event at,the center of the rotating folding element 409 has the advantage ofallowing the folding element 409 to be slightly smaller, than, forexample embodiments with more space between optical beams associatedwith different cores at the folding element surface. A smaller foldingelement means that the folding element 409 has the potential to spin ateven high speeds and the optical probe 406 can fit into smaller lumensor medical endoscope access ports.

In some embodiments, the distal optics 407 is placed approximately onefocal length from the center axis of the folding element 409 and thedistal facet of the multicore fiber 407 is imaged into the sample tissuewith a desired inverted magnification to achieve the desired spatialcoverage, the resolution, and the depth of field. In some embodiments,the distal optics 407 is placed approximately one focal length from thecenter axis of the folding element 409 and the distal facet of themulticore fiber 407 is imaged into the sample tissue with a desirednon-inverted magnification to achieve the desired spatial coverage,resolution, and depth of field. Inset illustration 412 illustrates adiagram of a coordinate-transformed representation of a helical scan. Aline 414 shows a conceptual path a central sample spot 413 would takealong a sample, in the unwrapped view, during a helical scan along thesample.

Detailed mathematical descriptions of the beam transformations relatingthe propagation of light from the distal end of the optical probe to thesample, as shown in the inset illustration 412, are shown in theappendix. These calculations illustrate how the optical probe system 401performs and can be optimized for a wide variety of applications.Specifically, these calculations help to illustrate how the relationshipbetween a shape, size and/or position of a core in the multicore fiber404 and a shape, size and/or position of an optical spot at the samplehave a known relationship. The calculations also illustrate how, as thepullback and/or rotational motions of the optical probe system 401progress, each optical spot will traverse a path that corresponds to aposition of a core in the multicore fiber. Using these knownrelationships between cores, optical sample spots, and traversed paths,a mathematical transformation can be performed in the controller 402that produces sample information.

A numerical example of the embodiment of the optical probe system 401illustrated in FIG. 4 including a multicore fiber that has beencommercially manufactured follows. The core-to-core spacing isapproximately 37 μm and the mode field diameter at the exit facet of themulticore fiber is about 10 μm at 1310 nm. A common size of lumen inhuman coronary arteries vessels can be ˜4 mm in diameter. A commonfull-width-half-maximum (FWHM) beam diameter at focus in the sampletissue in swept-source intravascular OCT systems is ˜25 um. This gives areasonable Rayleigh range (or confocal parameter) to measure the SS-OCTA-scan range over. Thus, having the distal optics 407 arranged toimplement a magnification of ˜2.5 can be useful and achieved withrelatively simple, small, and low-cost optical elements. Such opticstranslates the ˜10 um mode field diameter at the fiber distal facet to a˜25 um spot size near the vessel wall. In this simple example, thespot-to-spot spacing of the spot pattern 415 would be approximately37×2.5=92.5 um. The distances from the distal fiber facet to the lensplane, the lens focal length, and the distance from the lens plane tothe image (e.g. location of spot 413) are all governed by the lensequation (and more advanced versions of that equation) as is known inthe art, and can be set by the desired application. For example, oneapplication is imaging with in a coronary artery of ˜4 mm diameter orimaging within a balloon inflated esophagus or imaging with aswallowable or tethered capsule ˜20 mm in diameter.

Note that it can be beneficial to have this spacing denser and toachieve fiber cores more closely spaced than 37 um to allow a tightercluster of spots on the artery wall. If the core-to-core spacing in themulticore fiber 404 is too close, the light from one core will start tocouple or leak into the adjacent core. Many factors influence thisincluding the index of refraction profile in the cores and cladding andthe wavelength of light, but generally cross talk start to happen in asignificant way as the spacing gets near the mode field diameter. Butbecause the length of the multicore fiber 404 in endoscopic applications(˜1-2 m) is far less than that for typically telecommunicationapplications (10 m to many km), the cores can be more closely packedthan in telecommunications.

In some embodiments, it is possible to use a spinning or fixedwavelength dispersive device such as a grating in the folding element409. It should be understood that such a dispersive device can be usedin other embodiments of the present teaching as well. This produces aspatially separated set of patterns 415 at the sample, where eachspatially separated pattern 415 is at a different wavelength. Awavelength dispersive device allows the emission angle of the opticalbeams to be scanned via wavelength tuning of an optical source (orspatially dispersed if a broadband source is used instead of a tunablesource) in the system controller 402. This is analogous to a spectrallyencoded confocal microscopy (SECM) and other methods of wavelengthscanning. In these embodiments, the source in the system controller 402includes a wavelength tunable (or broad bandwidth) optical source. Theprocess of wavelength scanning from a diffraction grating or otherwavelength dispersive device is understood by those skilled in the art.Applying the wavelength scanning by including a dispersive element inrotating folding element 409 in combination with multicore fiber 404allow for much greater coverage of tissue in a given amount of time orprovide other valuable tissue information.

The equations for the beam translation described in detail in theAppendix are based on non-dispersive reflective devices. However, theseequations can be modified in a straightforward manner by those skilledin the art to include the grating properties that govern lightdiffraction by a dispersive element, such as a grating, in the foldingelement 409.

FIG. 5 illustrates an embodiment of an optical probe system 501 with amulticore fiber 504 having a hollow motor 510 of the present teaching.The optical probe system 501 includes a system controller 502 connectedto a patient interface unit 503 with a pullback capability. An opticalprobe 506 that contains a multi core optical fiber 504 with distaloptics 507 and a rotating distal motor 510. The motor 510 and thefolding element 509 are hollow to allow a fiber and/or light to passthrough the motor 510 and/or the folding element 509 to the distal endof the probe 506 where distal optics 507 are positioned. Thus, in thisconfiguration the hollow motor 510 and hollow fold mirror 509 arefollowed by a reflective and concaved distal optical element 507.

For simplicity, the light 508 emitted (or collected) from only one coreof the multicore fiber 504 is drawn but it should be understood that insome embodiments there may be more than one core in the multicore fiberand more than one light beam emitted and/or collected. It should beunderstood that some optical sample spots associated with a core maypropagate in the same optical beam (this can be viewed as a beam withina beam), so a number of beams is not necessarily the same as a number ofspots. As previously described, the distal facet of the multicore fibercan be cleaved or polished at an angle to form angled distal facet 504′.As described herein, the outer sheath of probe 506 can be opticallytransparent. Alternatively, in some embodiments a transparent windowshown in the dotted line of 520 can be utilized. One advantage of thisapproach is that there are fewer or, in some embodiments no, electricalor mechanical structures in the path of the optical beams as theyscan/rotate around the circumference of the optical probe. Suchstructures can cause outages in the imaging or sensing capability of thesystem. In some embodiments of the earlier diagrams there are electricaland/or mechanical connections from the controller or PIU to the distalmotor that can cause signal dropouts as the light beam sweeps throughthose areas.

An alternative embodiment of a configuration for the elements at the endof probe 506 is shown as inset illustration 530. This embodiment stillhas a distal optic 507, and can function without having a signal dropoutfrom sweeping thorough electrical or mechanical elements but does sowithout having a hollow motor like 510 or hollow prism like 509 as shownconceptually within the inset illustration 530. Here the multicore fiberis offset from the motor and the optical path from the multicore fiberlight emission (or collection) angle. The distal optic, and the foldmirror are arranged so that light freely propagates with no electricalor mechanical impediments.

As described herein, the folding element can be a wavelength diffractivereflective element that implements wavelength scanning in combinationwith rotational scanning and/or pullback scanning, instead of thereflective surface shown in folding element 507. The combination ofmulticore fiber, with rotational scanning, and wavelength scanning canallow for even more rapid scanning since it is possible to createtunable lasers that can run at speeds in excess of 1 MHz.

FIG. 6 illustrates an embodiment of an optical probe system 601 with amulticore fiber 604 configured for forward imaging of the presentteaching. The optical probe system 601 includes a system controller 602connected to a patient interface unit 603. In various embodiments, thePIU 603 may or may not include a pullback unit. An optical probe 606contains a multi core optical fiber 606 that is optically coupled todistal optics 607 and a rotating distal motor 610 that rotates a foldingelement 609. This optical probe system 601 is configured to allowforward imaging to a sample 611. In various embodiments, the sample 611may be a tissue or a target.

The optical probe system 601 uses a rotating distal motor 610 containinga folding element 609, which in some embodiments is a prism. The foldingelement 609 for these embodiments of forward imaging are generallytransparent to allow the optical beams 608 to pass through the element609. In the embodiment shown, the folding element 609 is bending thebeams upward. Inset illustration 612 partial view shows the foldingelement 609 in the end of the probe 606 turned by 180 degrees when thefolding element 609 is bending the beams 608 downward. Letters A, B, Crefer to beams as they exit the folding element 609 from a side core,the center core, and another side core, respectively. In contrast tosome of the configurations shown herein, this forward imaging patterndoes not have the outer light beams emitted from the probe 606 (such asA and C) rotating 360 degrees around the center light beam B, but rathereach light beam rotates in its own approximately circular fashion. Insetillustrations 620 and 621 show examples of the circular paths traced bythe centers of the optical sample spots at the sample plane. Eachoptical sample spot in the optical sample spot pattern traces anapproximately circular loop and those loops may (620) or may not (621)overlap and, if they overlap, the degree of overlap may vary, dependingon dimensions and optical elements involved for the particularapplication. Thus, the path traversed across the sample is a circularloop. The center beam, if any, behaves similarly to all others. Thesolid circles illustrating the paths of the optical sample spots shownin inset illustrations 620 and 621 correspond to the beams A, B, C shownin the other views of FIG. 6 , and the dotted circles correspond tobeams from other cores propagating beams that are not shown in the otherviews.

The embodiment shown in FIG. 6 illustrates how different paths foroptical sample spots can be achieved using different configurations ofoptical and mechanical elements in the optical probe system 601. Opticalprobe systems of the present teaching rely on the predetermined paths ofthe optical sample spots being used in a transformation of collectedoptical data to produce measurement data for particular applications.

While not illustrated in FIG. 6 , it is understood that in someembodiments, the optical sample spots at the sample 611 may also have asize shape and/or position that are related to the size, shape and/orposition of the core associated with that optical sample spot. Theseattributes of the illumination and/or collection pattern can also beused as part of the transformation of the collected data in rendering adesired measurement at the output of the optical probe system 601 asdescribed herein.

As described herein, the PIU 603 may or may not have a pullback motor,but a known relationship exists between any pullback motion of the probe606 and a path traversed by an optical sample spot associated with acore in the multicore fiber 604 and/or a size, shape and/or position ofan optical sample spot at the sample 611.

As mentioned above, it is possible to use a wavelength diffractiveelement in the folding element 609 described in connection with FIG. 6 ,with or even without a rotating motor.

Various embodiments of the multicore fiber with distal motor accordingto present teaching have been described herein in connection with FIGS.2A-6 . It should be understood that various features described inconnection with a particular embodiment are not necessarily limited tothat embodiment. For example, embodiments that are described inconnection with reflective optical elements can also be realized withtransmissive optical elements while still practicing the associatedaspects of the present teaching. Similarly, embodiments that aredescribed in connection with transmissive optical elements can also berealized with reflective optical elements while still practicing aspectsof the present teaching. Various embodiments may operate with light thatis supplied to a sample and/or light collected from a sample while stillpracticing the present teaching. In general, it should be understoodthat the various embodiments described herein may be used in connectionwith various measurement and/or sensing and/or imaging applicationswhile still practicing of the present teaching.

In addition to the examples above, there are a wide variety of ways toconfigure the optical elements in the distal optics element, e.g. distaloptics element 107, 207, 307, 407 of FIGS. 2-4 , and the relativedistance from the distal optical element 107, 207, 307, 407 and thefolding element, e.g. folding element 209, 309, 409 of FIGS. 2-4 ,surface. The surface could be reflective or refractive orwavelength-angularly dispersive (e.g. grating). The surface could beflat or have optical power (e.g. focusing power), and can thereby setthe properties of light as it impinges onto the sample (e.g. spot size,depth of field, etc.). The descriptions above just represent a few ofthe many embodiments of optical probe system that include multicorefibers of the present teaching.

Some of the above description has focused on light emanating from onecore being directed toward the sample and retro reflected back into thatsame core. This is common in known conventional OCT embodiments. But itshould be understood that it is also possible to have light start fromone core and return in a different core and/or multiple cores. Suchapproaches can be used in OCT but are even more common in NIR imagingand diffuse wave spectroscopy and other optical imaging modalities. Itis also possible to use different wavelengths in any of the embodimentsdescribed herein. For example, to emit one wavelength and collect a oneor more different wavelengths, as is done is fluorescence or Ramanimaging. Multi-wavelength operation can be done in the same core or adifferent core of the multicore fiber.

FIG. 7 illustrates an embodiment of an optical probe system 701 with adistal scanner 710 of the present teaching. The simplified block diagramof the optical probe system 701 illustrates a forward imaging embodimentfor which a multicore fiber 704 is optically coupled to a distal X-Yscanner 710 and optional interface optics 711 that project light to asample 730. In various embodiments, the sample 730 may be a tissueand/or a target. It should be understood that the term “target” is meantto be a very general term that could be, for example, a car in a LiDARapplication or a wide range of other target and applicationpossibilities. Light from a system controller 702 is optically coupledto a multicore optical fiber 704 via PIU 703. In this embodiment, thePIU 703 may be very simple and contain, among other things, a simplemulticore fiber optical connector and no pullback mechanism. Forexample, applications such as ophthalmic imaging or a surgicalmicroscope or more standard microscopy where readily repeatedprocedure-by-procedure connections are not necessarily needed. In someembodiments, the optical connection is by a fusion splice. In acardiology or endoscopy applications, PIU 703 may be more complex andconfigured to support rapid and repeated procedure-by-procedureconnections. In some embodiments, the PIU 703 is configured such that anew, and optionally disposable, probe is connected for each procedure.

Only the essential components of optical probe system 701 are shown. Forexample, some well-known items, such as traditional optical, mechanical,and electrical connections associated with medical and nonmedicalinstruments are not shown. For example, system 701 could be a spectraldomain or swept source domain optical coherence tomography ophthalmicimaging system and the skins, housings, patient chin head rests,alignment adjustments and other items that are well known by thoseskilled in the art of design and use of commercial OCT systems are notshown in FIG. 7 for simplicity.

The distal optics 707 of the optical probe system 701 can take a varietyof forms in different embodiments. For example, there may be no distaloptical elements and the light beams from the distal end of multicorefiber 704 propagate toward scanner 710. As another example, lensesand/or other optical elements can be use in the distal optics 707. Thelenses and/or other optical elements may be formed using 3D printedoptics on the tip of multicore fiber 704. The 3D printed optics may besimilar to that discussed previously in connection with FIG. 2A. In someembodiments, the distal optics 707 may take the form of fusion splicedcombinations of coreless and graded index multicore fibers, ball lenses,injection molded microlens arrays, and/or other type of single ormulti-element lenses or lens arrays. The distal optics 707 transform theoptical outputs of the cores of the multicore fiber to be collimatedand/or imaged in a suitable way for the particular application. Theimage is formed in a plane that is positioned between the distal tip ofthe multicore fiber 704 and the target/tissue/sample 730 indicated bythe solid line. Light going from the multicore fiber 704 altered byoptional distal optics 707 is illustrated by arrows 708.

The multiple light beams, which are illustrated by arrows 708, aredirected to an X-Y scanner 710. There are a variety of types of X-Yscanners 710 that can be used. In one specific embodiment, the X-Yscanner 710 is an X-Y scanning galvanometer that is illustrated in insetillustration 710′. Such galvanometers are in common use in ophthalmicOCT imaging devices. Such galvanometers are also used in various typesof microscopes. There are a variety of geometries that can be used tocombine two single-axis scanning galvanometers either with, or without,relay lenses between the X and Y mirrors. One- or two-axis PZT,electromagnetic actuator-based devices, MEMs devices, or combinations ofdevices may also be used to implement the X-Y scanner 710.

The X-Y scanner 710 causes the light pattern to traverse a path acrossthe sample. The scanning transformation of light from a singlecore fiber(which might be the central fiber core of a multicore fiber 704) to thetissue using galvanometers and two axis mirrors is known in the art.Scanning issues, such as pincushion distortion, beam walk between the Xand Y galvanometer when they are paired without relay lenses, andangular magnification from scanning are known issues. It is, however,worth noting that, in contrast to the full rotation of the outer coresrelative to a central core that was described above (e.g. in connectionwith the description of FIG. 2A), the rotation resulting from an X-Yscanner 710 is different. For example, the rotation of the cores inpattern 215 illustrated in inset illustration 212 does not occur whenusing the particular X-Y scanner 710 shown in FIG. 7 . Also, the fullcircular patterns, as shown in either of the inset illustrations 620,621 of FIG. 6 do not occur when using the X-Y scanner 710. Rather, thescan pattern transformation depends on various factors, such as thegeometry of the multicore fiber 704, the configuration of the distaloptics 707, the implementation of X-Y scanner 710, the interface optics711 and other factors. However, the transformation is known a prioriand/or can be derived, such that it can be used to transform datacollected from a sample using light impinging onto the sample and/orcollected from the sample into useful measurement information. Somespecific examples of the transformations that can be realized with theX-Y scanner 710 are given below.

One feature of the present teaching is that the multicore fiber withdistal motor can be implemented as a microscope optical probe system. Insurgical microscopes, colposcopes, anterior chamber ophthalmologic,general microscopy, and other applications it is common to haveadditional interface optics 711 that are positioned distal to the X-Yscanner 710. In one embodiment, which is illustrated within the dashedbox of inset illustration 717, distal optics 707′ collimates theindividual outputs of each core of multicore fiber 704′. The lightpassing to and/or from the fiber 704′ is directed onto X-Y scanner 710′,which may be an X-Y scanning galvanometer. The light is then focusedonto to target 730′ by interface optics 711′. In this embodiment, thelight from the different cores emitted from (or collected into)multicore fiber 704′ focuses at roughly the same spot on sample 730′ butenters and/or exits from different angles.

As noted earlier, one feature of the present teaching is that it ispossible to have light both emitted and collected along the center coreof a multicore fiber and also to emit light from the center core andcollect light from one or more of the outer cores, or vice versa. Forexample, referring to FIG. 7 , it is possible to have light both emittedand collected along the center core shown in multicore fiber 704, 704′,704″ and also light emitted from the center core and collect light fromone or more of the outer cores, or vice versa. In general, it ispossible to measure one or more combinations of light emitted from aparticular core in multicore fiber 704, 704′, 704″ and then collectedfrom the same or different cores with an N×N matrix of possible inputand output patterns. Such information in the matrix of input and outputlight patterns of the cores can be important indicator of tissuestructure as highly scattering tissue is more likely to couple beyondthe fundamental back scattered mode as is known in near infraredimaging, OCT, and diffuse wave imaging.

In some embodiments, it is desirable to have the light impinging on asample at different locations. One approach to accomplish this isillustrated within the dashed box of inset illustration 718. In thisembodiment, there is a shared lens 707″, which in some embodiments, maybe a lens group between the distal facet of multicore fiber 704″ and theX-Y scanner 710″. If the X-Y scanner 710″ is located in a pupil plane(i.e. approximately one focal length in front of the lens 707″), thenthe light beams will be collimated and will mostly overlap in the X-Yscanner 710″. Another lens 711″, which in some embodiments is a lensgroup, can then be used to focus that light into the sample in distinctlocations at the target 730″.

While inset illustration 717 shows an example where the different beamsimpinge on the same target location at different angles, and insetillustration 718 shows an example where the different beams impinge ondifferent target locations, there are other embodiments where thedifferent beams impinge on different target locations and also atdifferent angles. That is, combinations of these embodiments arepossible, where one or more subsets of cores are configured to overlapand other subsets are configured to impinge at distinct, and/ornonoverlapping locations on the sample. Also, while inset illustration717 shows the light beams arriving at the X-Y scanner 710′ approximatelyin parallel, and inset illustration 718 shows the light beams arrivingat approximately the same spot at the X-Y scanner 710″, many otherarrangements are possible. For example, the light beams may meet at anX-Y scanner in a diverging pattern or in a converging pattern where thepoint of convergence is conceptually behind the X-Y scanner. Here again,light beams from different subsets of cores may also be configured toutilize these different patterns.

When the mirrors in the X-Y scanner 710, 710′, 710″ are moved, the setof target locations and/or set of target angles would also move.Conceptually, the set of different locations and/or angles wouldtypically move as a set, although the extent to which they move as aset, and the details of any distortion or size change or reflection,will depend on various factors, such as the optical elements, thedetails of the X-Y scanner, and the geometry involved. Known single-coreOCT devices can be thought of as corresponding to a center beam (i.e.the beam from the center core of a multicore system), and so thecalculations used for known single-core optical probe system can beadapted via a mathematical transformations to apply to the side beams aswell.

There are of course a wide variety of other possible combinations ofdistal optics 707, X-Y scanner 710, and interface optics 711 that can beused. These result in corresponding ways to transfer, image, magnify,and adjust the light from the multicore fiber 704 distal facet to thetarget 730. In many embodiments, the various optical elements will notbe simple single element lenses as shown in FIG. 7 but can be morecomplex elements including for example, multielement lenses and/orlenses including aspherical elements.

One feature of the multicore fiber with distal motor of the presentteaching is that it can be used for imaging of the human eye. FIG. 8illustrates an embodiment of imaging a human eye 802 using an opticalprobe system 801 according to the present teaching. FIG. 8 shows lightfrom a multicore optical fiber 804 imaging a human eye 802 where theindividual beams sample near the same spot on the retina. Thus, theoptical probe system 801 is suitable for imaging within the human eye802 including the retinal area. Light from multicore fiber 804 iscollimated by distal optics 807, and then directed to X-Y scanner 810.Interface optics 811 and 812 are arranged in a relay lens design torelay the optical plane near the center position between the X-Y scanner810 onto a plane near the pupil of the eye in order to minimizevignetting and maximize light passing through the pupil. The relay lensdesign also relays the light in a way that the light focuses onto theretina with the desired spot size and corresponding depth of field. Asis known by those skilled in the art, the lens properties of the eye(primarily the cornea and lens of the eye) play a strong role infocusing the light impinging on the cornea near the retinal surface.Since the diameter of the human pupil is limited (in both a dilated eye,or an undilated eye), there is a trade-off between the individual beamdiameters and the spacing of the beams and the size of the individualspots on the retina. For example, if there is only one fiber core, thebeam diameter impinging (or emitted) on to the cornea can fill the pupiland higher lateral spatial resolution can be achieved on the retina. Asthe number of cores increases, each beam must be reduced to fit withinthe pupil at the expense of lateral resolution on the retina.

FIG. 9A illustrates another embodiment of imaging a human eye using anoptical probe system 901 of the present teaching. In this embodiment,light from a multicore optical fiber 904 images a human eye 902 wherethe individual beams sample different spots on the retina. Thus, theoptical probe system 901 is suitable for imaging within the human eye902, including the retinal area. The light from the multicore fiber 904is collimated such that the X-Y scanner 910 is placed in a pupil planeof the fiber facet. In this instance, the term “pupil plane” refers to aplane where the light beams mostly spatially overlap.

There are many ways to optically achieve this pupil plane placement ofthe X-Y scanner 910 including having the multicore fiber 904 distalfacet positioned approximately at the effective back focal length behindlens 907 and the X-Y scanner 910 positioned approximately the effectivefront focal length in front of lens 907. In this way, the light beamsare collimated and impinge and overlap near the effective center of X-Yscanner 910. Interface optics 911 and 912 are arranged to relay thepupil near the center position between X-Y scanner 910 where the lightbeams spatially overlap onto a plane near the pupil of the eye 902 whereagain the light beams spatially overlap. There are numerous ways toachieve the relay imaging from the plane of X-Y scanner 910 to the planeof the pupil of the eye 902. The use of the relay lens in the opticalprobe system 901 has the advantage of allowing each of the light beamsfrom the multicore fiber to overlay in the pupil of the eye 902 and thusallows each light beam to have a wider diameter, as compared, forexample, to the diameter of light beams shown in FIG. 8 . The widerdiameter of the light beams can translate to a smaller spot size on theretina and thus higher lateral spatial resolution (and better use ofavailable optical signal power). In the embodiment of FIG. 9 , thecenter of spots does not overlap on the retina. As such, it is possibleto have relatively fast imaging time as the scan can cover more area dueto multiple receivers running in parallel each sampling a different areaon the retina.

The embodiment of the multicore fiber with distal motor FIG. 9 hassimilar features of the embodiment shown in inset illustration 718 ofFIG. 7 . In both these embodiments, the multiple light beams from themultiple cores impinge on multiple (different) target locations, therebyallowing faster scanning, either with multiple parallel receivers or afast-switched system, which is described further herein. The targetplane 730 shown in inset illustration 718 can be identified with aconceptual “intermediate” plane between optical elements 911 and 912 andthe optical element 912 and lens properties of the human eye 902together translates this intermediate plane onto the retina. The“intermediate” plane is conceptually indicated by the X-Y axes 913 shownin FIG. 9 . As described herein, when the mirrors in the X-Y scanner 910are moved, the beams will typically move as a set on this intermediateplane, which therefore means they also typically move as a set on theretina. Also as described herein, the extent to which they move as aset, and the details of any distortion or size change or reflection,will depend on the optical elements, the details of the X-Y scanner 910,the geometry involved, and, in case of the optical probe system 901embodiment of FIG. 9 , the properties of the human eye 902.

In one embodiment, the X-Y scanner 910 is programmed to perform arow-by-row scan of a desired target area of the retina. FIG. 9Billustrates a single-core, row-by-row scan pattern. FIG. 9C illustratesthe loci of the seven different target spots in a multi-core OCT systemin such a row-by-row scan. As shown, the coverage of the target area ismuch greater than in the single-core case of FIG. 9B. Alternatively, forthe single-core case to achieve similar coverage would require many morerows in the scan, which translate into a much slower scan. In theexample shown in FIG. 9C, the loci overlap, which means some retinalocations are scanned multiple times (by different beams) at differenttimes, which allows averaging to improve image quality, detection ofmotion via speckle decorrelation, etc.

In applications where overlapping of loci is considered undesirable(i.e. any added benefit does not justify the added systems costs), amulti-core fiber with only cores A, B, C (or only cores A, B, C, D, E)can be used, to minimize overlap (and potentially system cost).Alternatively, FIG. 9D shows a slightly different situation where theseven target locations are slightly rotated, in such a way that theirloci overlap much less during the row-by-row scan.

While the scan patterns of FIGS. 9B-D cover conceptual examples ofrow-by-row scanning, other scanning patterns (raster, serpentine,spiral, Lissajous, etc.) can be utilized. When other scanning patternsare utilized, similar calculations of a number of cores, core geometry,overlap, and coverage efficiency are applied. There are a wide varietyof types of multicore fiber in addition to the seven-core example shownin FIG. 9 including 1×N geometries (linear arrays), triangular patterns,circular patterns, and many others.

One aspect of the multicore fiber with distal motor of the presentteaching is the use of parallel spectral domain or swept source domainoptical coherence tomography receivers with receiver componentsintegrated on a shared integrated photonic circuit with a multicoreoptical fiber and an imaging arrangement. One such configuration can besimilar to that shown in FIG. 9 , which allows multiple beams emittedfrom (or collected) into a multicore fiber where there is a distal X-Yscanner, and optics are configured to allow multiple near collimatedbeam to overlap in part as they pass through the pupil of a human eyeand focus to different spots on the human retina. One advantage ofparallel receivers, for example parallel OCT receivers, is it allowsmore rapid scanning of tissue area.

Some embodiments of the present teaching utilize a fast optical switchto select optical beams. FIG. 10 illustrates an embodiment of an opticalprobe system 1001 including and X-Y scanner 1010 and an optical switch1037 of the present teaching. The optical probe system 1001 includes acontrol system 1002 that includes the optical switch 1037 and isconnected to PIU 1003. The PIU 1003 interfaces to a multicore fiber1004, distal optical 1007, optical scanner 1010, interface optics 1011,and to target 1030. In the control system 1002, the optical switch 1037allows a single receiver 1034 and DSP 1035 to receive and processoptical beams selected from different cores of multicore fiber 1004.

There are many ways to implement the fast-optical switch 1037. Forexample, a photonic integrated circuit (PIC) switch using a Mach Zehnderor other PIC switch topologies, LiNbO3 switches, and others may be used.The rate at which swept source lasers can scan can be very high. In someembodiments, the laser source 1040 can sweep much faster than the X-Yscanner 1010 can scan. As such, by having a fast-optical switch, it ispossible to have a simpler and lower cost structure for receiver 1034and still sample multiple tissue spots. This is in contrast to theembodiment described in connection with FIG. 3 where the output powercan be shared among the cores of the multicore fiber and the receiverscollect light in parallel.

In the optical probe system 1001 of FIG. 10 , all the transmit light issent to one core of multicore fiber 1004, and the signal from that coreis collected. Then, the optical switch 1037 switches to the next core ofmulticore fiber 1004 and the process is repeated. Thus, the opticalswitch 1037 is configured so the switching rate of the switch 1037 issynchronized to the collection rate of light from each core beingreceived by the receiver 1034. During this process, the X-Y scanner 1010can continue to scan. The swept source laser 1040 repetition rate iscoordinated with the switching rate of the optical switch 1037 to ensurethat the transitions of the laser 1040 and switch 1037 are synchronizedand the full sweep of the source 1040 is completed when the switch 1037has completed its connection. Light from the swept source 1040 iscoupled to splitter 1031. The splitter 1031 directs part of the light toa reference arm 1032. The reference arm 1032 may include a variabledelay to assist in matching the lengths between the sample arm and thereference arm as is known in the art of OCT.

Another part of the output of the splitter 1031 is sent to a circulator1033 and then to the optical switch 1037, which is connected to PIU1003. An output of the circulator is connected to receiver 1034. Themulticore fiber 1004, distal optics 1007, optical beams 1009, X-Yscanner 1010, optional interface optics 1011, and target 1030 aresimilar to those described in the earlier figures. Back reflected lightfrom the target 1030 is coupled into the interferometric receiver 1034and processed by DSP 1035 to extract information about the target (e.g.range, morphology, dimensions, birefringence, absorption, scattering,etc.).

In one embodiment, the optical source 1040 and the optical switch 1037are integrated onto a single photonic integrated circuit. In anotherembodiment, parts of the optical receiver 1034 and the optical switch1037 are integrated onto a single photonic integrated circuit. Bothapproaches for photonic integration have advantages, chief among them isthat tight physical integration and small size make synchronizationbetween scanning of the imaging and switching of the switch easier andachieve lower costs.

Although the embodiment of optical probe system 1001 shown in FIG. 10was described in terms of a swept source OCT system it should beunderstood that it is equally applicable to spectral domain OCT systemand other types of optical systems such as NIR, fluorescence, Raman,diffuse wave, and other optical imaging and sensing systems.

Appendix

This appendix presents relevant mathematical details of the path tracedby a optical sample spot such as 220 and 220′ in FIG. 2A. We solve herethe cases of FIG. 2 and FIG. 4 explicitly. While we only solved thesetwo cases, it is straightforward to those skilled in the art that theanalysis can be easily generalized to other embodiments. For example,the application to different mirror angles, other beam angles, otherphysical distances, multicore fiber geometries, motions and other designparameters is straightforward.

Note that in reality, optical spot 220 has a non-zero size becauseoptical beam 208 has a non-zero width. This description in this appendixmostly relates to the location of the spot, not its size, and especiallyrelates to how the location changes as the mirror rotates. The appendixdescribes details of the path traversed by an optical sample spot as afunction of the motion provided by the probe. Accordingly, the appendixidealizes the spot as a single dimensionless point (i.e. zero size), andthe beam as a 1-dimensional line or ray (i.e. zero width). Analternative and equivalent view is that this appendix solves for thelocation of the “center” of the actual optical spot, illuminated by the“chief” or “central” ray of the actual beam. In this appendix, the words“spot” and “beam” and the like will usually refer to their idealizedversions. The extension to include finite size optical sample spots withvarying size, shapes and/or relative positions is straightforward.

A.1 Mirror Frame and Basic Equations

Consider a three-dimensional reference frame with the origin being thefixed point on the mirror which does not rotate. This frame is referredto herein as “the mirror frame”. The z axis is positioned along thedirection of pullback, with +z being the direction from the distaloptics toward the mirror, and the x axis and y axis defined according tothe usual right-hand rule. Note that there is a slightly differentgeometry than the geometry shown in FIG. 1, 111 , where +z is in theother direction.

The center core has coordinates (x, y, z)=(0, 0, p) where p<0 and |p| isthe distance from the center core at the end of the distal optics to themirror center. A typical new “side” core will have coordinates (x, y,z)=(a, b, p)=(r cos ϕ, r sin ϕ, p) where (a, b) or equivalently (r, ϕ)represents its position with respect to the center core. Thus, therelative position of at least two cores at the distal facet of themulticore fiber corresponds to the mathematical mapping of the pathtraced by optical sample spots in a light pattern generated by themulticore fiber in the optical probe.

For the configurations shown in FIG. 2A (and ignoring at this point theeffects of distal optical element 207), the beam leaves the core andtravels in the +z direction, represented by the vector (0, 0, 1). Theequations for the beam are therefore: x=a, y=b, with z beingunconstrained. We will call the beam from the fiber to the mirror theincident beam, and the beam from the mirror to the lumen the reflectedbeam.

The mirror surface is described by its perpendicular vector N=(c, s, t)where for shorthand we write c=cos θ, s=sin θ; θ=the instantaneous angleof the rotating mirror; and t=represents the tilt of the mirror.

The angle between N and the +z axis is given by angle A where cos A=N(0,0,1)/|N|=t/√{square root over (c²+s²+t²)}=t/√{square root over(t²+1)}. In the case of FIG. 2A, A=135° and t=−1.

Given the vector N and the fact that the mirror (by convention) passesthrough the origin, the equation for the mirror surface is N (x, y,z)=cx+sy+tz=0.

A.2 Point of Reflection and Direction of Reflection

The beam hits the mirror at the intersection of all the equations, i.e.x=a, y=b, cx+sy+tz=0 or z=—(ca+sb)/t.

Let F and D be the unit-length vectors describing the direction of theincident beam and the reflected beam, respectively. (For example, F=(0,0, 1) in case of FIG. 2A.) Then, the following equation holds: D−F=2(−F·N)N/|N|² where N is the (not necessarily unit-length) perpendicularvector of the mirror surface. Solving this for FIG. 2A, we have

D=(0,0,1)−2tN/(t ²+1)=(−2tc/(t ²+1),−2ts/(t ²+1),1−2t ²/(t ²+1))

Note that the x and y components of D are proportional to (c, s) whichverifies the obvious fact that the incident beam, the vector N, and thereflected beam are all in the same rotational plane described by θ. Alsonote that for the configuration shown in FIG. 2A where t=−1 (i.e.A=135°), we have D=(c, s, 0) representing a 90° turn as expected.

A.3 Where the Reflected Beam Hits the Lumen

The lumen is modeled as an enclosing cylinder, centered at the origin,aligned along the z direction, with radius R. The equation for thecylinder is x²+y²=R² (with z unconstrained).

Note that, in reality, the lumen is only approximately a cylinder, andindeed the fine structure of the lumen (including potentially depthstructure) is usually what is being measured. This appendix models thelumen as a cylinder because it is mainly concerned with the locationwhere the beam hits the (idealized) cylinder, as measurements at thislocation reveal the fine structure (including potentially depthstructure) of the lumen at this location.

The reflected beam is fully characterized by its point on the mirror (a,b, −(ca+sb)/t) and its direction D. For the case of FIG. 2A, since t=−1and D=(c, s, 0), the reflected beam is described by the parametrizedposition (a+uc, b+us, ca+sb) where u is a free (positive) parameter.This beam hits the lumen at the point, which we will call the “contactpoint”, where

R ²=(a+uc)²+(b+us)² =u ² +u(2ac+2bs)+(a ² +b ²)

This is a quadratic equation in u which can be solved exactly to findthe illuminated point. An equivalent, and more intuitive,characterization uses (a, b)=(r cos ϕ, r sin ϕ) and the quadraticequation becomes:

R ² =u ²+2ru cos(ϕ−θ)+r ² =u ²+2ru cos Δ+r ²

where we introduced the shorthand variable Δ=ϕ−θ. Solving this quadraticexplicitly, we have u=√{square root over (R²−r² sin²Δ)}−r cos Δ.

A.4 The “Unwrapped” Cylinder

The equations in the previous sections (A.1-A.3) are all exact, and theygive the exact point in three-dimensional space where the reflected beamcontacts or illuminates the lumen. That is, these equations detail thepath traversed by an optical sample spot as a function of the motionprovided by the probe. However, it is customary in the art (and oftenconvenient for displaying information) to consider the “unwrapped”cylinder (sometimes known as en face view) and the locus of the contactpoint in this unwrapped cylinder.

The unwrapped cylinder is defined by cutting the cylinder open at allpoints where x=+R and then flattening it into a 2-dimensional space,characterized by two parameters: z and β, the angle (in the (x,y)-plane) with respect to the original cylinder. That is, a point (z, β)in the unwrapped cylinder is equivalent to the point (R cos β, R sin β,z) in the 3-D frame.

Note that it is sometimes customary in the art to use Rβ, a distancealong the cylinder circumference, instead of β as the second parameter.For this equivalent characterization, β should be measured in radians.

The contact point's exact location in 3-D space can be mapped to itsexact location in the (z, β) or (z, Rβ) view by equating (a+uc, b+us,ca+sb)=(R cos β, R sin β, z). In particular:

z=ca+sb=r cos Δ

However, the resulting formula for β is cumbersome. Certainapproximations greatly simplify the formula and provide helpful insightfor those skilled in the art to understand and optimize the inventionsdescribe here in a wide variety of medical and non-medical applications.

A.5 Helpful Approximations for β

In this analysis, some approximations are made to simply thecalculations. In a first approximation: Typically R>>r (i.e. the lumenradius is much greater than the distance between a side core and thecenter core of the fiber). Thus we have:

u=√{square root over (R ² −r ² sin²Δ)}−r cos Δ≈R(1−r ² sin²Δ/2R ²)−r cosΔ≈R−r cos Δ

where we have kept any r/R term but dropped all (r/R)² and higher orderterms.

As is well known in the art, for the single-core case β=θ, i.e. the beamhits the lumen at exactly the instantaneous angle of the rotatingmirror. For a side core, we model its angle β as a perturbation β=θ+α.

In a second approximation 2: since α is a small angular perturbation, wehave cos α≈1, sin α≈α, where we have kept any a term but dropped all α²and higher order terms.

Both approximations can be considered “linearizing” approximations,since they keep small linear terms but ignore even smaller quadratic andhigher order terms. Using these two approximations, we now equate the xand y components. For instance, equating the x component R cos(θ+α)=α+ucand using Approximation 1, we have:

Rcos θcos α − Rsin θsin α ≈ rcos ϕ + (R − rcos Δ)cos θ = rcos ϕ + Rcos θ − rcos θ(cos θcos ϕ + sin θsin ϕ) = Rcos θ + rcos ϕsin²θ − rcos θsin θsin ϕ = Rcos θ − rsin θsin Δ

Now the second approximation allows us to identify Rα≈R sin α≈r sin Δ=rsin(ϕ−θ).

Equating they components, R sin(θ+α)=b+us, and using the sameapproximations, lead to the same results.

In summary, in the (z, Rβ) view, the contact point is (r cos Δ, Rθ+r sinΔ), with the above approximations. This means that, as the mirrorrotates (θ changes), while the reflected center core beam's contactpoint moves simply according to Rθ (as is known in prior art), thereflected side core beam's contact point rotates around the centerbeam's contact point, in a circle of radius r and rotating according tothe angle Δ=ϕ−θ.

A.6 Pullback

So far, we have described the geometric equations in a frame attached tothe mirror. In practice, of course, the mirror (the wholecapsule/apparatus) moves within and along the lumen or naturalmechanical fixture guiding it. This can be easily handled by redefiningthe z=0 reference to be a fixed point along the lumen instead of thefixed point on the mirror. For example, if the capsule is pulled back atconstant speed v, then the reflected center core beam's contact point isnow (z₀−vT, Rθ) where T is time, and the reflected side core beam'scontact point is now (z₀−vT+r cos Δ, Rθ+r sin Δ), i.e., it still rotatesaround the reflected center core beam's contact point, (z₀−vT, Rθ). Notethat typically the mirror also rotates at constant angular velocity,e.g. θ=ωT, thereby giving the reflected side core beam's contact pointas (z₀−vT+r cos(ϕ−ωT) , RωT+r sin(ϕ−ωT)). This is illustrated in FIG.2A, illustration 212.

A.7 Exact Geometry of FIG. 4

The preceding sections (A.1-A.6) show a detailed solution for the caseof FIG. 2A, where the incident beam is in the +z direction, i.e. (0, 0,1). We now briefly solve the case of FIG. 4 , where each incident beamis aimed to hit the mirror at the origin. In practice, this allows avery small mirror, which in turn may allow higher angular velocity dueto relaxed mechanical constraints, and the endoscope to fit into evensmall lumens or access ports of medical or non-medical instruments.

The incident beam goes from (a, b, p) to (0,0,0) so the unit-vector forits direction is F=—(a, b, p)/k where k=√{square root over(a²+b²+p²)}=√{square root over (r²+p²)} is the normalizing factor. Theunit-vector for the reflected beam is:

D=F−2(F·N)N/|N| ²

As before, N=(c, s, t) is the perpendicular vector for the mirrorsurface. Therefore:

D={−(a,b,p)+2(ac+bs+pt)(c,s,t)/(t ²+1)}/k

Note that ac+bs=r cos Δ. Also, for the configuration shown in FIG. 4 ,the tilt angle between N and +z axis is A=135° and t=−1. Therefore, theabove simplifies slightly to:

D={−(a,b,p)+(r cos Δ−p)(c,s,−1)}/k

kD=(X,Y,−r cos Δ)

where for convenience, we define X=(r cos Δ−p)c−a and Y=(r cos Δ−p)s−b.

As before, the reflected beam can be parametrized by u. Since u is afree (positive) variable, it does not matter whether we include orexclude the positive rescaling factor k. Since the reflected beamoriginates from the origin (where the incident beam hits the mirror),the reflected beam is simply ukD. The contact point where the reflectedbeam hits the lumen is given by:

R ² =x ² +y ² =u ² {X ² +Y ²}

We can solve for the exact value of u as follows:

$X = {{{\left( {{r\cos\Delta} - p} \right)c} - a} = {{{\cos\theta\left\{ {{r\left( {{\cos\theta\cos\phi} + {\sin\theta\sin\phi}} \right)} - p} \right\}} - {r\cos\phi}} = {{{r\sin\theta\cos\theta\sin\phi} - {r\cos\phi\sin^{2}\theta} - {p\cos\theta}} = {{{r\sin\theta\sin\Delta} - {p\cos\theta Y}} = {{{\left( {{r\cos\Delta} - p} \right)s} - b} = {{{\sin\theta\left\{ {{r\left( {{\cos\theta\cos\phi} + {\sin\theta\sin\phi}} \right)} - p} \right\}} - {r\sin\phi}} = {{{r\sin\theta\cos\theta\cos\phi} - {r\sin\phi\cos^{2}\theta} - {p\sin\theta}} = {{{- r\cos\theta\sin\Delta} - {p\sin\theta X^{2}}} = {{{r^{2}\sin^{2}\theta\sin^{2}\Delta} - {2{rp}\cos\theta\sin\theta\sin\Delta} + {p^{2}\cos^{2}\theta Y^{2}}} = {{{r^{2}\cos^{2}\theta\sin^{2}\Delta} + {2{rp}\sin\theta\cos\theta\sin\Delta} + {p^{2}\sin^{2}\theta X^{2}} + Y^{2}} = {{{r^{2}\sin^{2}\Delta} + {p^{2}u}} = {R/\sqrt{p^{2} + {r^{2}\sin^{2}\Delta}}}}}}}}}}}}}}$

So the exact 3-D location of the contact point ukD=R(X, Y, −r cosΔ)/√{square root over (p²+r² sin² Δ)}. In particular, the z componentis:

z=−Rr cos Δ/√{square root over (p ² +r ² sin²Δ)}

This value is different from the value in FIG. 2A, which is describedmore in connection with A4 in two ways. First there is a rescalingfactor of u=R/√{square root over (p²+r² sin² Δ)}, and second, there is anegative sign. Both will be explained more fully in the next section.

A.8 Approximations for FIG. 4 and the Unwrapped View

As before, we now map the exact 3-D location onto the unwrapped viewcharacterized by (z, Rβ) and as before, some approximations will greatlyhelp with intuitive understanding.

In a third approximation, since the mirror surface is at 45°, we musthave |p|>r or else the incident beam would be behind the mirror surface.In practice, we often have |p|>>r. Therefore, once again we will“linearize” the model and ignore any (r/|p|)² and higher order terms.This allows us to simplify √{square root over (p²+r² sin² Δ)}≈√{squareroot over (p²)}=|p|=−p (recalling that p is negative by convention), andas a result, u≈R/|p|.

Using this approximation, we have z≈−Rr cos Δ/|p|.

Next we equate the x component, and use the second approximation:

Rcos β = Rcos (θ + α) = Rcos θcos α − Rsin θsin α ≈ Rcos θ − Rαsin θ = uX ≈ R(rsin θsin Δ − pcos θ)❘p❘ = Rcos θ + Rrsin θsin Δ/❘p❘

This allows us to identify Rα≈−Rr sin Δ/|p|.

For completeness, we now equate the y component with the sameapproximations:

Rsin β = Rsin θcos α + Rcos θsin α ≈ Rsin θ + Rαcos θ = uY ≈ R(−rcos θsin Δ − psin θ)/❘p❘ = Rsin θ − Rrcos θsin Δ/❘p❘

which again allows us to identify Rα≈−Rr sin Δ/|p|.

In summary, in the (z, Rβ) view, the contact point is (−Rr cos Δ/|p|,Rθ−Rr sin Δ/|p|), with the above approximations. This means that, as themirror rotates (θ changes), while the reflected center core beam'scontact point moves simply according to Rθ (as is known in prior art),the reflected side core beam's contact point rotates around the centerbeam's contact point, in a circle of radius Rr/|p| and rotatingaccording to the angle Δ=ϕ−θ.

Referring to FIG. 2A, which was described in connection with A.4-A.5,the radius of rotation of the contact point is no longer r, but insteadis Rr/|p|. This can be best described by visualizing the “cone” formedby the incident beams from the multiple side cores. This cone has a baseof radius r, and has its apex at the origin which is distance |p| away,with an apex angle=2 arctan(r/|p|). The reflected beams also form a conewith its apex at the origin, with the same apex angle. Therefore, as thereflected cone hits the lumen which is approximately distance R away,the projection onto the lumen is an approximately circular base ofradius rescaled by a factor of R/|p|, i.e. a radius of Rr/|p|. Insummary, the two cones are similar in the geometric sense (subject tothe approximations).

Mathematically, the contact point of FIG. 2A and the contact point ofFIG. 4 are exactly half a circle apart, as evidenced by the minus signsin (−Rr cos Δ/|p|, Rθ−Rr sin Δ/|p|). However, this does not materiallyaffect the efficacy of either embodiment, as such sign changes will behandled by the proximal unit's computations.

Sections A.7-A.8 use the mirror frame. Similar to section A.6, pullbackof the FIG. 4 scenario (i.e. movement with respect to the lumen frame),can again be easily incorporated as (z₀−vT−Rr cos Δ/|p|, Rθ−Rr sinΔ/|p|), or by assuming θ=ωT, as (z₀−vT−Rr cos(ϕ−ωT)/|p|, RωT−Rrsin(ϕ−ωT)/|p|.

A.9 Concluding Remarks on the Mathematical Treatment in this Appendix

Section A.1-A.6 solved the configuration described in connection withFIG. 2A, with incident beams in the +z or (0,0,1) direction. SectionA.7-A.8 solved the configuration described in connection with FIG. 4 ,with incident beams converging at the origin. While the exact 3-Dsolutions for the contact points are described, the exact solutions arecumbersome. The approximate unwrapped view gives a much more intuitivepicture of the side contact points rotating around the center contactpoint, while the center contact point traces an (unwrapped) line in the(z, Rβ) view. These are illustrated in FIGS. 2 and 4 respectively.

If the incident beams are at some other angles, the equations in thisappendix can be modified to describe them, and similar approximationscan be used to understand them intuitively. However, an even simplerapproximate understanding can be obtained if we simply view the mirror,not as reflecting the incident beams, but as providing virtual beamsources behind the mirror that shine through the mirror. For example, ifthe incident beams are start at z-distance |p| away as usual andconverge at a point z-distance q in front of the mirror, then byconsidering the two similar cones from the virtual sources, through theconvergence point, to the contact points on the lumen, we again have twosimilar cones (subject to approximations). Referring to FIG. 4 , therelative “heights” of the cones are |p|: R. In the new example, therelative “heights” will be (|p|−|q|):(R+|q|). As a result, the side corebeam's contact points will still (approximately) rotate around thecenter core beam's contact point, but now with a radius of(R+|q|)r/(|p|−|q|).

Similarly, if the incident beams converge at a point z-distance q′behind the mirror, the new radius of rotation for the side core beams'contact points will be (R−|q′|)r/(|p|+|q′|), provided R>|q′|. Cases ofR<|q′| or cases of the incident beams diverging can be similarly handledby considering basic geometry using the virtual sources. Indeed FIG. 2Ais the special case of the incident beams neither converging nordiverging and equivalent to taking q′=+∞.

As long as the mirror surface is 45° (angle A=135° and tilt t=−1), thecircle formed by the virtual beam sources and the circle formed by thereal beam sources (at the end of the fiber/optics) will beperpendicular, which means the reflected beam cone will be perpendicularto the z-axis. However, if the mirror surface is not 45° (tilt t #−1),then the two circles will no longer be perpendicular. In this case thereflected beam cone will not be perpendicular to the z-axis, and theprojection onto the lumen (in the unwrapped view) will be approximatelyan ellipse instead of approximately a circle. However, the side corebeams' contact points will still rotate around center core beam'scontact point, although in an (approximately) elliptical circuit.

In summary, although FIG. 2A and FIG. 4 are sample embodiments, theanalysis in this appendix can be extended to include other lengths andother beam angles and mirror angles

EQUIVALENTS

While the Applicant's teaching is described in conjunction with variousembodiments, it is not intended that the Applicant's teaching be limitedto such embodiments. On the contrary, the Applicant's teachingencompasses various alternatives, modifications, and equivalents, aswill be appreciated by those of skill in the art, which may be madetherein without departing from the spirit and scope of the teaching.

What is claimed is:
 1. An optical probe imaging system comprising: a) anoptical probe; b) a multicore optical fiber positioned in the opticalprobe and having a proximal and a distal end; c) distal optics that areoptically coupled to the distal end of the multicore optical fiber, thedistal optics imaging light propagating in the multicore optical fiberso as to generate a light pattern on a sample that is based on arelative position of at least two cores at a distal facet of themulticore optical fiber; d) a distal motor mechanically coupled to theoptical probe so that a motion of the distal motor causes the lightpattern to traverse a path across the sample; e) an optical receiverhaving an input that is optically coupled to the proximal end of themulticore optical fiber, the optical receiver receiving light that hastraversed the path across the sample and generating an electrical signalcorresponding to the received light; and f) a processor having an inputcoupled to an output of the optical receiver, the processor mapping theelectrical signal to a representation of information about the sample,wherein the mapping is based on the relative position of at least twocores at the distal facet of the multicore fiber and on the motion ofthe distal motor.
 2. The optical probe imaging system of claim 1 whereinthe mapping is further based on a rotation rate of the distal motor. 3.The optical probe imaging system of claim 1 wherein the mapping isfurther based on a pullback speed of the optical probe.
 4. The opticalprobe imaging system of claim 1 wherein the relative position of atleast two cores is such that a spot from one of at least two cores and aspot from the other of at least two cores visits a nominally sameposition at the sample at different times.
 5. The optical probe imagingsystem of claim 1 wherein the relative position of at least two cores issuch that a spot from one of the at least two cores traverses a circularloop path pattern across the sample and a spot from the other of the atleast two cores traverses a circular loop path pattern across thesample.
 6. The optical probe imaging system of claim 5 wherein thecircular loop path pattern of the one of the at least two cores and thecircular loop path pattern of the other one of the at least two coresoverlap.
 7. The optical probe imaging system of claim 5 wherein thecircular loop path pattern of the one of the at least two cores and thecircular loop path pattern of the other one of the at least two cores donot overlap.
 8. The optical probe imaging system of claim 1 wherein thedistal motor includes a galvanometer.
 9. The optical probe imagingsystem of claim 1 wherein the distal motor is a hollow motor.
 10. Theoptical probe imaging system of claim 1 wherein the distal motor is anX-Y scanner.
 11. The optical probe imaging system of claim 10 whereinthe X-Y scanner is configured such that light impinges on a sample attwo different locations.
 12. The optical probe imaging system of claim10 wherein the X-Y scanner is configured such that the light patternoverlaps least in part across the sample.
 13. The optical probe imagingsystem of claim 1 wherein the optical probe imaging system is an opticalcoherence tomography system.
 14. The optical probe imaging system ofclaim 1 wherein the optical receiver includes a photonic integratedcircuit.
 15. The optical probe imaging system of claim 14 wherein thephotonic integrated circuit comprises a plurality of optical receiverson a single photonic integrated circuit.
 16. The optical probe imagingsystem of claim 1 further comprising an optical switch optically coupledto the proximal end of the multicore fiber.
 17. The optical probeimaging system of claim 16 wherein a switching rate of the opticalswitch is synchronized to a collection rate of received light by thereceiver.
 18. The optical probe imaging system of claim 16 wherein theoptical switch includes a photonic integrated circuit.
 19. The opticalprobe imaging system of claim 1 further comprising a folding elementpositioned adjacent to the distal optics, the folding element directinglight propagating in the multicore optical fiber to the sample.
 20. Theoptical probe imaging system of claim 19 wherein the mapping is furtherbased on an angle of a perpendicular vector of a surface of the foldingelement with respect to a center of the optical probe.
 21. The opticalprobe imaging system of claim 19 wherein the folding element includes anon-planar surface.
 22. The optical probe imaging system of claim 19wherein the distal motor is mechanically coupled to the folding element.23. The optical probe imaging system of claim 1 further comprising awavelength dispersive device positioned adjacent to the distal optics atthe distal end of the multicore optical fiber, the wavelength dispersivedevice separating wavelengths of light propagating in the multicoreoptical fiber.
 24. The optical probe imaging system of claim 1 whereinthe optical probe is configured to translate so that it advances towardsthe sample and pull backs from the sample.
 25. The optical probe imagingsystem of claim 24 further comprising a motor that translates theoptical probe.
 26. The optical probe imaging system of claim 24 whereinthe mapping is further based on a speed that the optical probetranslates.
 27. The optical probe imaging system of claim 1 furthercomprising a motor mechanically coupled to the optical probe thattranslates the optical probe to advance the optical probe towards thesample and to pull back the optical probe from the sample.
 28. Theoptical probe imaging system of claim 1 further comprising an opticalsource having an output that is coupled to the proximal end of themulticore optical fiber.
 29. The optical probe imaging system of claim28 wherein the optical source is a swept optical source and the opticalreceiver is a swept source domain optical coherence tomography receiver.30. The optical probe imaging system of claim 1 wherein the distal endof the multicore fiber is formed with an angled distal facet thatreduces back reflection.
 31. An optical probe imaging system comprising:a) an optical probe; b) a singlecore optical fiber positioned in theoptical probe and having a proximal end and a distal end comprising anangled facet; c) a rotatable non-planar folding element opticallycoupled to the distal end of the singlecore optical fiber, the rotatablenon-planar folding element redirecting and focusing light propagating inthe singlecore optical fiber so as to generate a light pattern on asample; d) a distal motor mechanically coupled to the rotatablenon-planar folding element so that a motion of the distal motor causesthe light pattern to traverse a path across the sample; e) an opticalreceiver having an input that is optically coupled to the proximal endof the singlecore optical fiber, the optical receiver receiving lightthat has traversed the path across the sample and generating anelectrical signal corresponding to the received light; and f) aprocessor having an input coupled to an output of the optical receiver,the processor mapping the electrical signal to a representation ofinformation about the sample, wherein the mapping is based on the motionof the distal motor.
 32. The optical probe imaging system of claim 31wherein the rotatable non-planar folding element comprises a concavesurface.
 33. The optical probe imaging system of claim 31 wherein therotatable non-planar folding element comprises a refraction element. 34.The optical probe imaging system of claim 31 further comprising distaloptics positioned between the singlecore optical fiber and the rotatablenon-planer folder element.
 35. A method of imaging a retina, the methodcomprising: a) propagating a plurality of light beams through amulticore optical fiber from a proximal end to a distal end; b)projecting the plurality of light beams emerging from the distal end ofthe multicore optical fiber to overlap at least in part onto atwo-dimensional scanner; c) scanning the plurality of light beams in afirst and a second direction with the two-dimensional scanner; d)imaging the scanned plurality of light beams onto a plurality of spotson the retina; e) imaging a portion of the plurality of light beams thatis reflected by the retina back to the multicore fiber; f) propagatingthe reflected portion of the plurality of light beams back through themulticore optical fiber; and g) receiving the plurality of reflectedlight beams at the proximal end of the multicore optical fiber.
 36. Themethod of claim 35 further comprising directing selected ones of theplurality of reflected light beams to a single receiver.